High temperature alloy steel and articles made therefrom



Patented Feb. 25, 1947 HIGH TEMPERATURE ALLOY STEEL AND ARTICLES MADE THEREFROM Charles '1. Evans, Jr., Titusville, Pa., asslgnor to Universal-Cyclops Steel Corporation, Bridgeville. Pa... a corporation of Pennsylvania No Drawing. Application November 8, 1943,

" Serial No. 509,473

Claims.

The object of this invention is the production of an alloy steel having good load-carrying ability at high temperatures. In recent years there have been developed machines such as superchargers, gas turbines, etc., in which certain parts are sub- Jected to fairly high stresses which must be withstood at high temperatures over a considerable length of time. In fact, the life of a supercharger or gas turbine is limited by the load-carrying ability of the parts which are subject to stress at high temperatures. The parts are also required to resist the corrosive attack of combustion gases at the high temperatures.

I have discovered an alloy which has unique and peculiar load-carrying abilities at high temperatures and is therefore especially adapted for such purposes. It is an alloy steel containing as essential alloying constituents silicon, manganese. chromium, nickel. tungsten, molybdenum, columbium and titanium, together with carbon in certain balanced proportions which I have found required to produce the unique load-carrying ability.

The steel has carbon and its alloying constituents within the following ranges:

C .20- 35 Mn .40- l 25 Si .40- .70 Cr 18.00-20.00 Ni ace-10.00 W 1.00- 1.50 Mo 1.00- 1.50 Cb .15- .45 T1 .10- .40 S Max. .04 P Max. .04

The typical analysis which I have found to be useful for general purposes is as follows:

It will be noted that the alloying constituents of the steel amount to only about 30 odd percent of the alloy. The ratio of high temperature loadcarrying ability to the total of alloying elements is the highest of any material known to me. Particularly with regard to carbide and ferrite forming constituents, small quantities of a num-- ber of different alloying elements have proven to be more efl'ective than larger amounts of a few.

This alloy can be readily formed into the desired shapes by forging, rolling and casting.

When properly fabricated and treated this material meets the following specifications:

(0) A high-temperature load-carrying ability through 1350' F. which so far as I am aware is exceeded by no known wrought materials and only equaled by analyses of much higher alloy content.

(b) High-temperature load-carrying ability through 1500 P. which so far as I am aware is equaled or exceeded only by much more highly alloyed wrought and cast materials.

(0) The material is also suitable for low tress service through 1800" F.

(d) The above typical analysis is balanced to contain about 5% or less of ferrite phase. The normal commercial structure consists essentially of a fine-grained austenitic matrix with carbides. The normal composition is susceptible to the effects of cold work or hot-cold-work to produce exceptionally high strengths. The load-carrying ability is also improved from the hot worked condition by solution treatments at high temperatures followed by soaking at intermediate temperatures and/or hot-cold-work.

(e) The above analysis is not susceptible to precipitation hardening effects to any appreciable degree. It possesses a high degree of surface and structural stability.

(f) This analysis may be softened (annealed) by rapid cooling from high temperatures. A. stress-relief anneal at intermediate temperatures preserves the as-worked properties and promotes machinability.

(a) The alloy is quite readily machinable and exceeds many of the more familiar austenitic alloys in machinability.

(h) Adequate surface oxidation resistance is obtained through 1800 F. The material is exceptionally resistant to grain boundary oxidation even as high as 2400 F. and the inherently fine grain structure is retained even after prolonged soaking at high temperatures. This line grain structure is an aid to fatigue resistance.

(i) The material has an exceptionally high modulus of rigidity. This may have a bearing on its unusual load-carrying ability.

(1') It possesses a high degree of resistance to both reducing and oxidizing corroding media and Short-time tensile tests at room temperature (80 F.)

Brinell hardness 235 Yield strengths, lbs. per sq. in., at

.02% offset 55,000 .10% offset 65,000 20% oiiset 75,000

Ultimate tensile strength, lbs. per sq. in 110,000 Elongation, per cent 25 Reduction in area, percent 40 Short-time tensile tests at elevated temperatures ii R d ti tens e e uc on Elongation 'lem F. strength, in area, D lbs. sq mm per cent Room (80 F.) 110,000 25 40 500 l00,000 25 40 750.. 95,000 25 40 1,000. 90.000 25 40 1,10)... 86,01!) 25 40 1,330. 75,000 25 40 1,300. 65,000 30 45 1, 100v 00,000 30 45 1,500 55,0) 30 45 Long-time stress-to-rupture tests lime re- Reduction Elongation quired to in area of Temp, F. produce ruptured ruptured per sq. n m sample, sample per cent firs. per cent 00,000 35 1,1!) 48,000 100 10 20 40,000 1,000 5 10 50.000 10 1,350 32,000 Ii!) 10 2) 20,000 1,000 5 10 35,000 10 25 35 1.500 20,000 100 10 20 11,500 1.000 5 l0 Alloys coming within the composition ranges set forth above possess these same general physical properties as the alloy of the specific analysis set forth but to varying degrees, depending not only on processing variables but also depending on the balance of the two general classes of alloying elements within the compositions: (1) carbide and ferrite formers, (2) austenite formers.

The carbide and ferrite formers are chromium, molybdenum, tungsten, columbium. titanium and silicon. Molybdenum is the most influential ferrite former and the proportions of ferrite can be best controlled by manipulating this element. An increase in any or all of these ferrite and carbide formers tends to promote the presence of ferrite. When ferrite is present the following metallurgical properties are enhanced:

(1) Retention of ductility under load at elevated temperatures. Transcrystalline fractures are produced. This is a unique and valuable feature in engineering materials for classes of elevated temperature service.

(2) A fine-grained structure is promoted.

(3) Resistance to intergranuiar corrosion,

(4) Machinability.

(5) Weldability.

(6) Fatigue endurance ratio.

(7) Coeillcient of thermal expansion is lowered.

(8) Thermal conductivity is increased.

(9) General stability of structure is promoted. The material is less susceptible to processing variables.

(10) Precipitation hardening effects are held to a minimum.

The austenite formers are carbon, nickel and manganese. These elements are effective in forming austenite in the order named with carbon being by far the most influential constituent in this regard. An increase in any or all of these austeniteformers tends to inhibit the presence of ferrite and insure a uniform structure of austenite and carbides, and therefore enhance the following metallurgical properties:

(1) Maximum response to processing variables such as cold or hot-cold-work, solution treatments, aging treatments or combinations of these processes.

(2) workability is improved.

(3) Maximum short-time elastic properties can be produced.

(4) Resistance to creep is promoted.

(5) Precipitation hardening and solution treating effects are promoted.

(6) Coefllcient of thermal expansion is increased.

(7) Thermal conductivity is lowered.

The metallurgical composition and physical properties of my alloy steel may be varied within somewhat wider limits than those set forth above while still securing good load-carrying ability at high temperatures.

The alloy may be made within the following composition:

C .15- Mn .40- 3 00 Si .40- 2 00 Cr 18.00-23.00 Ni 6.00-20.00 W .75- 2.00 M0 .75- 2.00 Cb .15- 1.50 Ti .10- 1.00 S Max. .25 P M83. .10

Even somewhat wider ranges may be employed while still retaining good load-carrying ability at high temperatures within the following range of compositions:

C .15- 1.00 Mn .40- 5.00 Si .25- 3.00 Cr 14.00-28.00 Ni 4.0040110 W .50- 3.00 Mo .50- 4.00 Cb .10- 2.50 Ti .10- 2.00 S Max. .40 P Max. .20

In melting these compositions the columbium is usually supplied in the form of ferro-columbiuru and may be accompanied by a minor amount of tantalum. Thus in the analyses listed above the columbium contents given may actually include a small percentage 01 tantalum (usually not over of the columbium content given). This is permissible because the tantalum has an eflect approximately equivalent to that or columbium.

The remainder of the various analyses set forth above is substantially iron and elements which are not subversive to the action of the essential alloying elements there enumerated in producing good load-carrying ability at elevated temperatures. The balance may be substantially commercial steel which may contain the usual impurities, residuals or minor amounts of alloying elements coming from the scrap or introduced durlng the melting, deoxidation, etc., of the alloy. The usual impurities, residuals or minor amounts or alloying elements are not subversive to the action of the essential alloying elements above enumerated in producing good load-carrying ability at elevated temperatures. The alloy may also contain other alloying elements, particularly cobalt and nitrogen, which are not subversive to the action of the essential alloying elements above enumerated in producing good load-carrylng ability at elevated temperatures.

T'he alloy can be made in accordance with the usual melting practice of the alloy steel industry. The usual procedure is to cast the metal into. ingots and forge or roll it into billets or slabs.

. The billets and slabs are then hot formed into the desired shapes which are then stress relieved by soaking at intermediate temperatures or annealed by rapid cooling from high temperatures. By stress relieving is meant the heating through of the entire section to arrive at a uniform temperature. This standard treatment has been found to increase the machinability of the alloy over the as-worked or annealed condition.

If the soaking time at intermediate tempera-' tures is extended beyond that required for stress relief, the treatment may be considered as an attempt to produce precipitation hardening effects. Such further treatment, while it may lower the load-carrying ability at elevated temperatures, has been found to further increase machinability.

The high temperature load-carrying ability of the alloy may be altered by solution treatments. These solution treatments consist of soaking for various time periods at temperatures in excess of 1800 F., followed by either rapid or slow cooling, and/or subsequent soaking and/or cold-work or hot-cold-work at intermediate temperatures.

My alloy is particularly useful for the manuiacture of articles which require high load-carrying ability at elevated temperatures, such, for example, as the blading and rotors for gas turblues and superchargers, internal combustion engine valves, safety and relief valves, and other parts which are subject to high temperatures and stresses. Most of such parts also require resistance against corrosion at high temperatures, which resistance is supplied by the alloy. While the alloy can be readily forged, rolled and machined in the making of machine parts, it also may be made into castings,

While I have specifically described the preferred embodiments of my invention, it is to be understood that the invention is not so limited but may be otherwise embodied and practiced within the scope of the following claims.

I claim:

1. An alloy steel characterized by high load- 1.25%, silicon .40 to chromium 18.00 to- 20.00%, nickel 8.00 to 10.00%, tungsten 1.00 to 1.50%, molybdenum 1.00 to 1.50%. columbium .15 to .45% and .titanium .10 to .40% as essential constituents, sulphur .04% maximum and phosphorus .04% maximum, the balance being substantially all iron and elements which are not.

subversive to the action of the essential. constituents in imparting good load-carrying ability at elevated temperatures.

3. Articles which require high load-carrying ability at elevated temperatures formed from an alloy steel containing carbon about 28%, manganese about .75%, silicon about .55%, chromium about 19%, nickel about 9%. tungsten about 1.25%, molybdenum about 1.25%, columbium about 30%, and titanium about 25% as essential constituents, sulphur .04% maximum and phosphorus .04% maximum, the balance being substantially all iron and elements which are not subversive to the action of the essential constituents in imparting good load-carrying ability at elevated temperatures.

4. Articles which require high load-carrying ability at elevated temperatures formed from an alloy steel containing carbon .20 to .35%, manganese .40 to 1.25%, silicon .40 to 310%, chromium 18.00 to 20.00%, nickel 8.00 to 10.00%, tungsten 1.00 to 1.50%, molybdenum 1.00 to 1.50%, columbium .15 to .45%, and titanium .10 to .40% as essential constituents, sulphur 04% maximum and phosphorus 04% maximum, the balance being substantially all iron and elements which are not subversive to the action of the essential constituents in imparting good load-carrying ability at elevated temperatures.

5. An alloy steel containing carbon .15 to .35%, manganese .40 to 3.00%, silicon .40 to 200%, chromium 18.00 to 23.00%. nickel 8.00 to 20.00%, tungsten .75 to 2.00%, molybdenum .75 to 2.00%, columbium .15 to 1.50%, and titanium .10 to 1.00% as essential constituents, sulphur .04% maximum and phosphorus .04% maximum, the balance being substantially all iron and elements which are not subversive to the action of the essential constituents in imparting good load-carrying ability at elevated temperatures, said steel having a structure consisting predominantly of an austenitic matrix together with minor proportions of ferrite and carbide and characterized by great resistance to deformation and rupture under load at high temperatures together with retention of ductility under load.

6. Articles which require high load carrying ability at elevated temperatures formed from an alloy steel containing carbon .15 to .35%, manganese .40 to 3.00%, silicon .40 to 2.00%, chromium 18.00 to 23.00%, nickel 8.00 to 20.00%. tungsten .75 to 2.00%, molybdenum .75 to 2.00%, columbium .15 to 1.50%, and titanium .10 to 1.00% as essential constituents, sulphur .04%

REFERENCES CITED The following references are of record in the 16 tile oi this patent:

Certificate of Correction Patent No. 2,416,515.

Number UNITED STATES PA'I'ENTB Name Date Krivobok Aug. 2, 1988 Krivobok Aug. 9, 1938 Becket May 23, 1939 Franks May 23, 1939 Mohling Apr. 10, 1945 (filed Jan. 23, 1943) OTHER REFERENCES Kinzel 8: Franks, Alloys of Iron and Chromium, vol. 11, pages 435, 436 and 437. Published N. Y.. 1940 by McGraw-Hill Book 00.

February 25, 1947.

CHARLES T. EVANS, JR.

It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows: Column 6, line 53, claim 5, for

200% read 2.00%; column and comma and phosphorus 04% mammum,; l

and that th phos lilhorus .04% maximum, and; with t in the Patent Oflioe.

7, line 1, claim 6 aftermaximum ines 5 and 6, same claim, strike out c said Letters Patent should be read ese corrections therein that the same may conform to the record of the case insert the words Signed and sealed thislfith day of April, A. D. 1947.

LESLIE FRAZER,

First Assistant Uommiaaioner of Patents.

REFERENCES CITED The following references are of record in the 16 tile oi this patent:

Certificate of Correction Patent No. 2,416,515.

Number UNITED STATES PA'I'ENTB Name Date Krivobok Aug. 2, 1988 Krivobok Aug. 9, 1938 Becket May 23, 1939 Franks May 23, 1939 Mohling Apr. 10, 1945 (filed Jan. 23, 1943) OTHER REFERENCES Kinzel 8: Franks, Alloys of Iron and Chromium, vol. 11, pages 435, 436 and 437. Published N. Y.. 1940 by McGraw-Hill Book 00.

February 25, 1947.

CHARLES T. EVANS, JR.

It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows: Column 6, line 53, claim 5, for

200% read 2.00%; column and comma and phosphorus 04% mammum,; l

and that th phos lilhorus .04% maximum, and; with t in the Patent Oflioe.

7, line 1, claim 6 aftermaximum ines 5 and 6, same claim, strike out c said Letters Patent should be read ese corrections therein that the same may conform to the record of the case insert the words Signed and sealed thislfith day of April, A. D. 1947.

LESLIE FRAZER,

First Assistant Uommiaaioner of Patents. 

